In a 6–3 decision, the Court sided with the government,[2] ruling that the exclusion order was constitutional. Six of eight Roosevelt appointees sided with Roosevelt. The lone Republican appointee, Owen Roberts, dissented. The opinion, written by Supreme Court justice Hugo Black, held that the need to protect against espionage outweighed Fred Korematsu's individual rights, and the rights of Americans of Japanese descent. (The Court limited its decision to the validity of the exclusion orders, adding, "The provisions of other orders requiring persons of Japanese ancestry to report to assembly centers and providing for the detention of such persons in assembly and relocation centers were separate, and their validity is not in issue in this proceeding.") During the case, Solicitor GeneralCharles Fahy is alleged to have suppressed evidence by keeping from the Court a report from the Office of Naval Intelligence indicating that there was no evidence that Japanese Americans were acting as spies or sending signals to enemy submarines.[3]

The decision in Korematsu v. United States has been very controversial.[2] Korematsu's conviction for evading internment was overturned on November 10, 1983, after Korematsu challenged the earlier decision by filing for a writ of coram nobis. In a ruling by Judge Marilyn Hall Patel, the United States District Court for the Northern District of California granted the writ (that is, it voided Korematsu's original conviction) because in Korematsu's original case, the government had knowingly submitted false information to the Supreme Court that had a material effect on the Supreme Court's decision.

The Korematsu decision has not been explicitly overturned, although in 2011 the Department of Justice filed official notice,[4] conceding that it was in error, thus erasing the case's value as precedent for interning citizens. However, the Court's opinion remains significant both for being the first instance of the Supreme Court applying the strict scrutiny standard to racial discrimination by the government and for being one of only a handful of cases in which the Court held that the government met that standard.

On May 19, 1942, during World War II, Japanese Americans were compelled to move into relocation camps by Civilian Restrictive Order No. 1, 8 Fed. Reg. 982. This order, and other similar orders, were based upon Executive Order 9066 (February 19, 1942).

Fred Korematsu was a Japanese-American man who decided to stay in San Leandro, California and knowingly violated Civilian Exclusion Order No. 34 of the U.S. Army. Fred Korematsu argued that the Executive Order 9066 was unconstitutional and that it violated the Fifth Amendment to the United States Constitution. He was arrested and convicted. No question was raised as to Korematsu's loyalty to the United States. The Circuit Court of Appeals affirmed the conviction, and the Supreme Court granted certiorari.

The decision of the case, written by Justice Hugo Black, found the case largely indistinguishable from the previous year's Hirabayashi v. United States decision, and rested largely on the same principle: deference to Congress and the military authorities, particularly in light of the uncertainty following Pearl Harbor. Justice Black further denied that the case had anything to do with racial prejudice:

Korematsu was not excluded from the Military Area because of hostility to him or his race. He was excluded because we are at war with the Japanese Empire, because the properly constituted military authorities feared an invasion of our West Coast and felt constrained to take proper security measures, because they decided that the military urgency of the situation demanded that all citizens of Japanese ancestry be segregated from the West Coast temporarily, and, finally, because Congress, reposing its confidence in this time of war in our military leaders — as inevitably it must — determined that they should have the power to do just this.

According to my reading of Civilian Exclusion Order No. 34, it was an offense for Korematsu to be found in Military Area No. 1, the territory wherein he was previously living, except within the bounds of the established Assembly Center of that area. Even though the various orders issued by General DeWitt be deemed a comprehensive code of instructions, their tenor is clear, and not contradictory. They put upon Korematsu the obligation to leave Military Area No. 1, but only by the method prescribed in the instructions, i.e., by reporting to the Assembly Center. I am unable to see how the legal considerations that led to the decision in Hirabayashi v. United States, 320 U.S. 81, fail to sustain the military order which made the conduct now in controversy a crime. And so I join in the opinion of the Court, but should like to add a few words of my own.

The provisions of the Constitution which confer on the Congress and the President powers to enable this country to wage war are as much part of the Constitution as provisions looking to a nation at peace. And we have had recent occasion to quote approvingly the statement of former Chief of the justice Justice Hughes that the war power of the Government is "the power to wage war successfully." Hirabayashi v. United States, supra, at 93, and see Home Bldg. & L. Assn. v. Blaisdell, 290 U.S. 398, 426. Therefore, the validity of action under the war power must be judged wholly in the context of war. That action is not to be stigmatized as lawless because like action in times of peace would be lawless. To talk about a military order that expresses an allowable judgment of war needs by those entrusted with the duty of conducting war as "an [p225] unconstitutional order" is to suffuse a part of the Constitution with an atmosphere of unconstitutionality. The respective spheres of action of military authorities and of judges are, of course, very different. But, within their sphere, military authorities are no more outside the bounds of obedience to the Constitution than are judges within theirs. "The war power of the United States, like its other powers . . . is subject to applicable constitutional limitations," Hamilton v. Kentucky Distilleries Co., 251 U.S. 146, 156. To recognize that military orders are "reasonably expedient military precautions" in time of war, and yet to deny them constitutional legitimacy, makes of the Constitution an instrument for dialectic subtleties not reasonably to be attributed to the hard-headed Framers, of whom a majority had had actual participation in war. If a military order such as that under review does not transcend the means appropriate for conducting war, such action by the military is as constitutional as would be any authorized action by the Interstate Commerce Commission within the limits of the constitutional power to regulate commerce. And, being an exercise of the war power explicitly granted by the Constitution for safeguarding the national life by prosecuting war effectively, I find nothing in the Constitution which denies to Congress the power to enforce such a valid military order by making its violation an offense triable in the civil courts. Compare Interstate Commerce Commission v. Brimson, 154 U.S. 447; 155 U.S. 3, and Monongahela Bridge Co. v. United States, 216 U.S. 177. To find that the Constitution does not forbid the military measures now complained of does not carry with it approval of that which Congress and the Executive did. That is their business, not ours.

Justice Frank Murphy issued a vehement dissent, saying that the exclusion of Japanese "falls into the ugly abyss of racism," and resembles "the abhorrent and despicable treatment of minority groups by the dictatorial tyrannies which this nation is now pledged to destroy". He also compared the treatment of Japanese Americans with the treatment of Americans of German and Italian ancestry, as evidence that race, and not emergency alone, led to the exclusion order which Korematsu was convicted of violating:

I dissent, therefore, from this legalization of racism. Racial discrimination in any form and in any degree has no justifiable part whatever in our democratic way of life. It is unattractive in any setting, but it is utterly revolting among a free people who have embraced the principles set forth in the Constitution of the United States. All residents of this nation are kin in some way by blood or culture to a foreign land. Yet they are primarily and necessarily a part of the new and distinct civilization of the United States. They must, accordingly, be treated at all times as the heirs of the American experiment, and as entitled to all the rights and freedoms guaranteed by the Constitution.

Justice Murphy's two uses of the term "racism" in this opinion, along with two additional uses in his concurrence in Steele v. Louisville & Nashville R. Co., decided the same day, are among the first appearances of the word "racism" in a United States Supreme Court opinion. The first appearance was in Justice Murphy's concurrence in Ex parte Endo, 323 U.S.283 (1944).[5] The term was also used in other cases, such as Duncan v. Kahanamoku, 327 U.S.304 (1946) and Oyama v. California, 332 U.S.633 (1948). It then disappeared from the court's lexicon for 18 years — it reappeared in Brown v. Louisiana, 383 U.S.131 (1966). It did not appear in Loving v. Virginia, 388 U.S.1 (1967),[6] even though that case did talk about racial discrimination and interracial marriages.

By contrast, Justice Robert Jackson's dissent argued that "defense measures will not, and often should not, be held within the limits that bind civil authority in peace," and that it would perhaps be unreasonable to hold the military, who issued the exclusion order, to the same standards of constitutionality that apply to the rest of the government. "In the very nature of things," he wrote, "military decisions are not susceptible of intelligent judicial appraisal." He acknowledged the Court's powerlessness in that regard, writing that "courts can never have any real alternative to accepting the mere declaration of the authority that issued the order that it was reasonably necessary from a military viewpoint."

He nonetheless dissented, writing that, even if the courts should not be put in the position of second-guessing or interfering with the orders of military commanders, that does not mean that they should have to ratify or enforce those orders if they are unconstitutional. Indeed, he warns that the precedent of Korematsu might last well beyond the war and the internment:

A military order, however unconstitutional, is not apt to last longer than the military emergency. Even during that period, a succeeding commander may revoke it all. But once a judicial opinion rationalizes such an order to show that it conforms to the Constitution, or rather rationalizes the Constitution to show that the Constitution sanctions such an order, the Court for all time has validated the principle of racial discrimination in criminal procedure and of transplanting American citizens. The principle then lies about like a loaded weapon, ready for the hand of any authority that can bring forward a plausible claim of an urgent need. Every repetition imbeds that principle more deeply in our law and thinking and expands it to new purposes.

Jackson acknowledged the racial issues at hand, writing:

Korematsu was born on our soil, of parents born in Japan. The Constitution makes him a citizen of the United States by nativity and a citizen of California by residence. No claim is made that he is not loyal to this country. There is no suggestion that apart from the matter involved here he is not law abiding and well disposed. Korematsu, however, has been convicted of an act not commonly a crime. It consists merely of being present in the state whereof he is a citizen, near the place where he was born, and where all his life he has lived. [...] [H]is crime would result, not from anything he did, said, or thought, different than they, but only in that he was born of different racial stock. Now, if any fundamental assumption underlies our system, it is that guilt is personal and not inheritable. Even if all of one's antecedents had been convicted of treason, the Constitution forbids its penalties to be visited upon him. But here is an attempt to make an otherwise innocent act a crime merely because this prisoner is the son of parents as to whom he had no choice, and belongs to a race from which there is no way to resign. If Congress in peace-time legislation should enact such a criminal law, I should suppose this Court would refuse to enforce it.

In sum, Justice Jackson's opinion advocates an almost hermetic separation between the judicial and military spheres in wartime. While he probably would not issue an injunction against an illegal military order while it was taking place, he could not give it any sanction afterwards, and thus voted to reverse Mr. Korematsu's criminal conviction for violating the order he felt was illegal.

Former Supreme Court Justice Tom C. Clark, who represented the U.S. Department of Justice in the "relocation," writes in the Epilogue to the book Executive Order 9066: The Internment of 110,000 Japanese Americans (written by Maisie and Richard Conrat):

The truth is, the writ of habeas corpus shall not be suspended, and despite the Fifth Amendment's command that no person shall be deprived of life, liberty or property without due process of law, both of these constitutional safeguards were denied by military action under Executive Order 9066...

But the late Supreme Court Chief Justice, William H. Rehnquist had a somewhat different view. He had this to say in his 1998 book All the Laws But One – Civil Liberties in Wartime, p. 124: "An entirely separate and important philosophical question is whether occasional presidential excesses and judicial restraint in wartime are desirable or undesirable. In one sense, this question is very largely academic. There is no reason to think that future wartime presidents will act differently from Lincoln, Wilson, or Roosevelt, or that future Justices of the Supreme Court will decide questions differently than their predecessors."

On May 20, 2011, Acting Solicitor General Neal Katyal released an unusual statement denouncing one of his predecessors, Solicitor General Charles H. Fahy.[7] He accused Fahy of having “suppressed critical evidence” in the Hirabayashi and Korematsu cases before the Supreme Court during World War II.

The historical record shows that the allegedly suppressed document, known as the Ringle Report, did not originate within "the Office of Naval Intelligence," but was written by a junior intelligence officer in the field and was specifically disavowed by the Office of the Chief of Naval Operations in a letter to the FBI dated February 14, 1942. The letter enclosed a copy of the report, and stated that the report “…does not represent the final and official opinion of the Office of Naval Intelligence.”[8] Only two years after the "internment" did the FCC and FBI officially state they had found no evidence of collaborationist radio transmissions by Japanese Americans being sent from the West Coast, but they did find some evidence of such illicit radio transmissions from Hawaii.[9] Accordingly, it was long felt that any suspicion of "suppression of evidence" by Solicitor General Fahy was ill-advised. Korematsu's vindication in 1983, however, was a ruling that the internment was fatally flawed.

Katyal remarked in 2011 that, in the pre-war era of ethnic segregation in public accommodations, which on the West Coast included wide refusal of equal treatment of "Japs," the Chief's office was easily prejudiced to disavow the Ringle Report in its 1942 letter. He noted that Fahy's subordinates had actually alerted Fahy in writing that failing to investigate that report, or at least to disclose its existence in the briefs or argument in the Supreme Court, “might approximate the suppression of evidence.” Thus, Katyal concluded that Mr. Fahy “did not inform the Court that a key set of allegations used to justify the internment” had been doubted, if not fully discredited, within the government's own agencies.

Katyal therefore announced his office's filing of a formal "admission of error" negating the precedent value of the Supreme Court decision the government had thereby won. He reaffirmed the extraordinary duty of the Solicitor General to address the Court with "absolute candor," due to the "special credence" the Court explicitly grants to his court submissions.[10]

^For photocopy of the letter see "MAGIC: The Untold Story of U.S. Intelligence and the Evacuation of Japanese Residents from the West Coast During WWII." Loman, David, Asst. to the Director, National Security Agency. Athena Press, Inc. 2001 ISBN 0-9602736-1-1 Page 314